I've seen patterns for both, and it just really bugs me. Some patterns have you chain before turning for the next row, and others have you chain after turning. Is there a reason, or is it just personal preference?

__________________Wenda"Be afraid of bears, of bungee-jumping, of faulty wiring in old houses, but never, ever be afraid of trying something in knitting."Stephanie Pearl-McPhee, Knitting Rules

Actually, the order you do it in makes little difference. A turn and chain will look the same as a chain and turn. Either way the chain will have a twist. Sometimes that twist will make it a bit more difficult to work in the top of the turning chain at the end of a row.

When come to turning and rising chains, if I am turning I will remove my hook from the loop and insert it from the other side, then turn and chain. This will help prevent the chain from twisting.

Most of the time it is just personal choice if you like to chain and turn or if you prefer to turn and chain.

If the hook slips during the turn you may find a chain and turn more friendly if you accidentally FROG. It is easier to see how many chains were lost to the FROG than from a complex crochet stitch.